Internal combustion engine manufacturers are constantly seeking to increase power output and fuel efficiency of their products. One method of generally increasing efficiency and power is to reduce the oscillating mass of an engine, e.g., of the pistons, connecting rods, and other moving parts of the engine. Efforts to increase engine power and/or efficiency also may also result in an increase in pressure and/or temperature within the combustion chamber during operation.
Engines, and in particular the pistons of the engine, are therefore under increased stress as a result of these reductions in weight and increased pressures and temperatures associated with engine operation. Piston cooling is therefore increasingly important for withstanding the increased stress of such operational conditions over the life of the engine.
To reduce the operating temperatures of piston components, a cooling gallery may be provided about a perimeter of the piston. A coolant such as crankcase oil may be introduced to the cooling gallery, and may be distributed about the cooling gallery by the reciprocating motion of the piston, thereby reducing the operating temperature of the piston.
At the same time, the cooling galleries may increase overall complexity of the piston assembly and manufacturing of the same. For example, cooling galleries may require additional component, such as a cooling gallery cover, in order to encourage proper circulation of a coolant throughout the cooling gallery by temporarily trapping coolant (e.g., oil) that is circulated through the cooling gallery. The additional components such as cover plates also add complexity, however. Additionally, cooling galleries may be expensive and/or difficult to form in smaller piston applications such as in the case of lightweight or light duty pistons. Known methods of forming enclosed cooling galleries in one-piece pistons, such as friction welding, also require extremely high strength piston components to properly form the piston and cooling gallery features without unintended deformation during the friction welding process, thereby increasing size and weight of the resulting pistons. The large magnitude forces placed on the piston components during the friction welding process also limits where the weld joints may be located.
Accordingly, there is a need for a piston that minimizes overall piston weight and manufacturing complexity, while also allowing adequate cooling, such as by providing a cooling gallery.